

A156181


Number of solutions to e(1)*1 + e(2)*2 + ... + e(n)*n = e(1)*1 + e(2)*2 + ... + e(n)*n, where e(j) are from {1,0,1}, j=n,...,n.


1



1, 3, 13, 65, 403, 2669, 18759, 136477, 1020373, 7785741, 60395165, 474817833, 3775005799, 30298719855, 245167429681, 1997854542163, 16381233095985, 135050690760831, 1118800428892925, 9308791880014333, 77755512086256649
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OFFSET

0,2


COMMENTS

a(n) = coefficient of x^(n*(n+1)) in the polynomial Product_{k=1..n} (1 + x^k + x^(2*k))^2, and is the maximal such coefficient as well.


LINKS

Ray Chandler, Table of n, a(n) for n = 0..1052 (terms < 10^1000)
Steven R. Finch, Signum equations and extremal coefficients, February 7, 2009. [Cached copy, with permission of the author]


MATHEMATICA

Table[Coefficient[Expand[Product[(1 + x^k + x^(2*k))^2, {k, 1, n}]], x, n*(n + 1)], {n, 0, 20}]


CROSSREFS

Cf. A007576, A047653, A063865.
Sequence in context: A199143 A002468 A198663 * A260783 A228987 A112807
Adjacent sequences: A156178 A156179 A156180 * A156182 A156183 A156184


KEYWORD

nonn


AUTHOR

Steven Finch, Feb 05 2009


STATUS

approved



